Apparatus for humidifying a gas flow

ABSTRACT

In a device for humidifying a gas flow, an atomized liquid is combined with a gas flow in a spray chamber, and passed through a generally U-shaped gas flow passage having a first generally vertical part  3  through which the atomized liquid and gas passes to a lower part  4.  From there, the gas passes generally vertically upwardly to an outlet  9.  The lower part of the passage incorporates an opening  6  to a water separator  7.  The opening  6  is closable by a float device  10,  or includes a flow restricting control valve  13.

This application is a national stage of International Application No.PCT/EP2006/008904, filed Sep. 13, 2006, the entire disclosure of whichis herein expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to apparatus for humidifying a gas flow,including means for separating excess water from the gas flow. Theinvention is particularly but not exclusively applicable for humidifyingfuel gas and oxidant gas used in a fuel cell for automotiveapplications.

A known type of fuel cell has a polymer electrolyte membrane in whichhydrogen forming a fuel gas is passed over one side of the membrane (theanode). In response to an applied electrical load an electrochemicalreaction takes place in which hydrogen ions migrate through the membraneto combine with oxidant (usually derived from air) on the other side (orcathode) of the membrane. It is necessary for both the hydrogen gas andthe air, which are kept in separate streams, to be humidified to ensurethat a necessary quantity of water passes through both sides of the fuelcell where it serves to enhance the electrochemical action and also toprevent the drying out of the membrane, which would lead to poorefficiency in the electrochemical reaction and damage the fuel cell, orat least reduce its service life.

German patent document DE 100 28 133.8 discloses apparatus which isparticularly suitable for humidifying a process gas flow in a fuel cellsystem. The humidified device comprises three sections, a spray chamber,a heat exchanger region, and a water separator. Water is atomized andinjected into the spray chamber, where it is mixed with the flow of thegas. In the heat exchange region, heat exchange means are provided whichutilize the heat in the gas to at least partially evaporate water tohumidify the gas and to enable the excess water to be at least partiallycondensed. To ensure that satisfactory humidification takes place, agreater amount of water is atomized than is theoretically required toachieve a relative humidity of the gas of 100 percent. The excess wateris collected in a water collector or separator located below the heatexchanger region.

The humidified device and water separator described have disadvantageswhen used in an automotive application, in particular, in coping withthe g-forces which occur during cornering and changes in angularposition of the vehicle when the vehicle is on a sloping surface. Thiscan lead to inefficient drainage and reduced water separation. Thus,excess water can lie on the bottom of the separator where it can bere-entrained by the gas flow and, in extreme conditions, an excess ofwater can enter the fuel cell, reducing its efficiency.

One object of the present invention is to provide a humidifyingapparatus incorporating a water separator, which is much less sensitiveto g-forces than the known device.

This and other objects and advantages are achieved by the humidificationapparatus according to the present invention in which an atomized liquidis combined with a gas flow in a spray chamber to humidify the gas. Thecombined atomized liquid and gas are passed through a gas flow passagewhich comprises a generally U-shaped passage having a first generallyvertical part through which the atomized liquid and gas stream pass to alower part. From there, the gas stream passes generally verticallyupwardly to an outlet. According to a feature of the invention, thelower part of the passage incorporates an opening through which excesswater separated out from the gas stream can pass to a water separator.The opening is closable by a float device, or includes a water flowcontrol valve which permits water to flow into the chamber butsubstantially impedes water flow from the chamber back into the gas flowpassage.

Preferably, the float device controls a drain valve which controls theflow of liquid out of the water separator. In a preferred embodiment,the opening is at the lowermost part of the gas flow passage, and isrelatively small compared to the cross-section of the passage and thatof the water separator chamber (reservoir). In this way, water readilydrains through into the water separator and reduces the amount of waterthat is exposed to the gas flow and is subject to possiblere-entrainment. The water in the water separator is preferablytransferred for use elsewhere in the fuel cell operating system for, forexample, humidifying the incoming gas.

In another embodiment, the water separator chamber is substantiallysquare or rectangular in plan view having a planar top wall which, inthe installed condition on a vehicle is substantially horizontal. Fouropenings are located adjacent the four corners of the top wall, whichforms the lower wall of the lowermost part of the gas flow passage.Preferably, each of the four openings includes a flow control valveincorporating a baffle to restrict the flow of water in a direction fromthe chamber to the gas passage.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a gas flow passage in ahumidifier, together with a water separator;

FIG. 2 is a side view of FIG. 1;

FIGS. 3 a 3 b, and 3 c show schematically in plan view, threealternative layouts of single, double, and multi-outlet designs of waterseparator;

FIG. 4 is a sectional side view of the embodiment of FIG. 3 c; and

FIG. 5 is a detail view of a water flow control valve used in theembodiment of FIGS. 3 c and 4.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a gas flow passage 1 of a fuel gas humidifier, togetherwith a water separator 2. The further details of such a fuel gashumidifier are familiar to those skilled in the art. For example, inGerman Patent application DE 100 28 133.8, mentioned previously, fuelgas for a fuel cell, typically hydrogen, is mixed with atomized water ina spray chamber. The combined fuel gas and atomized water (whichconsists of a large number of water droplets) passes through a heatexchanger, where the water droplets are partially evaporated to humidifythe gas and partially condensed into water and larger water droplets.

In the present embodiment, the combined gas and atomized water and thewater droplets then pass through a generally U-shaped flow passage,first passing downwardly through a first generally vertically disposedgas flow passage section 3 to reach the lowermost part 4 of the passage1. The latter is formed in a shaped section having inclined sides 5 toreduce the cross-sectional area of the passage in the downwardlyvertical sense. The lowermost part terminates in an opening 6 leadinginto the water separator chamber 7.

In the lowermost part 4 of the passage, the gas flow is forced through a180 degree turn to rise up an outlet part 8 of the gas flow passage toan outlet 9 leading to the input of a fuel cell. Thus, the opening 6into the water separator chamber 7 is relatively small compared to becross-section of the gas flow passage so that the possibility of waterdroplets being re-entrained by the gas flow is substantially reduced.The opening 6 is generally on the centerline of the water separatorchamber 7 and is also much smaller than the cross-sectional area of thewater separator chamber, to reduce the possibility of water in theseparator chamber re-entering the gas flow passage when the vehicle'smotion generates g-forces that disturb the water in the chamber. Thechamber may incorporate baffles to reduce the tendency of the liquid inthe chamber to surge excessively.

Additionally, the efficiency of separating out the water droplets fromthe humidified gas stream is increased because the effect ofgravitational forces, which tend to draw the water droplets downwardly,is increased by the reversal of the gas flow. That is, the greater massof the water droplets compared to the gas increases the rate at whichthey drop out of the gas, in the manner of a centrifugal separator.

The opening 6 from the gas flow passage into the water separator 7 iscontrolled by a float 10 in the shape of a ball which is adapted toclose off the opening 6 if the water in the water separator rises abovea predetermined level. Should this occur, the float 10 also may serve tooperate a valve (not shown) which opens to allow water to drain out ofthe separator. In normal operation, the condensed water is drawn out ofthe water separator by a pump and recirculated to humidify the incomingfuel gas or oxidant supplied to be fuel cell.

The present design, having the U-shaped gas flow passage with the narrowopening to the water separator placed immediately beneath, enables theoverall size and height of the humidifier/water separator assembly to bereduced substantially compared with the known devices referred toearlier. The design also facilitates the draining of all water out ofthe system so that it is far less likely to be damaged by ice formationwhen the vehicle is not in use under freezing conditions. The use offloats to close the opening into the water separator chamber has furtheradvantages when water from both sides of the fuel cell (that is, thefuel gas side and the airflow side) can be vented into a common waterseparator chamber. The use of the floats to close the openings to thegas flow passages serves to prevent the two different gases fromentering the wrong passage from the water separator chamber.

FIG. 2 shows an arrangement in which two water separator chambers 7 aand 7 b are provided spaced across the lowermost part of the gas flowpassage 4. In an alternative form, as indicated by the dotted line 11,two flow passages may be provided side-by-side in a common housing: onefor humidifying the fuel gas, and the other for humidifying the airsupply providing the oxidant for the fuel cell. In this case, excesswater in the process gases on both sides of the membrane are vented intoa common water separator chamber.

FIG. 3 a shows the opening of a single chamber water separator, whileFIG. 3 b shows two openings which lead into a common water separatorchamber 7 (although they may lead into separate chambers), and FIG. 3 cshows an arrangement having four openings all opening into a commonwater separator chamber 7.

FIG. 4, is a sectional side view of the embodiment shown in FIG. 3 c, inwhich four openings 6 open into a common water separator chamber 7. Thefour openings are spaced apart towards the four corners of the chamber 7which is substantially square or rectangular in plan. Instead of theclosable float valve 10 described in the embodiment of FIGS. 1 and 2,the openings in this embodiment each incorporate a water flow controlvalve 13, further details of which are shown in FIG. 5. The controlvalves 13 have a venturi-shaped bore with a center section 14 of reduceddiameter, and tapered inlet and outlet sections 15 and 16. The lower endof the center section adjacent to the chamber 7 has a flow-restrictingbaffle 17 with one or more bores of a relatively small diameter. In thisway, water impinging on the top wall 18 of the chamber 7, which formsthe lower wall of the gas flow passage 3, can flow down through thecontrol valves, but the baffle 17 serves effectively to prevent waterrising up back into the gas flow passage.

When the apparatus is installed in a vehicle, the wall 18 is locatedsubstantially in a horizontal position. The use of four spaced apartflow control valves ensures that whether the vehicle is tilted laterallyfrom one side to the other or fore and aft, or is subjected to g-forceslaterally or fore and aft, any water separating out from the gas streamwill flow on to an area of the wall 18 containing an open control valveso that the water can drain down into the chamber 7. With thisarrangement, it has been found that although a degree of gas can passinto the chamber 7, this does not affect the efficient functioning ofthe separator.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1-8. (canceled)
 9. A device for humidifying a gas flow, by combining itwith an atomized liquid in a spray chamber, and passing it through a gasflow passage, wherein: the gas flow passage is generally U-shaped, andhas a first generally vertical part through which the atomised liquidand gas stream passes to a lower part, from which it passes generallyvertically upwardly to an outlet; the lower part of the passage has anopening for passing excess water separated from the gas stream, to awater separator chamber; the opening has one of a float device forclosing it off, and a water flow control valve which permits water toflow into the chamber but substantially impedes water flow from thechamber back into the gas flow passage.
 10. The device according toclaim 9, further comprising a valve for controlling the flow of liquiddraining out of the water separator.
 11. The device according to claim9, wherein the float device controls a drain valve which controls theflow of liquid out of the water separator chamber.
 12. The deviceaccording to claim 9, wherein: the opening is situated at the lowermostpart of the gas flow passage; and the opening is relatively smallcompared to the cross-section of the passage and the cross-section ofthe water separator chamber.
 13. The device according to claim 9,wherein a plurality of openings lead from the gas flow passage into thewater separator chamber.
 14. The device according to claim 13, wherein:the water separator chamber is substantially square or rectangular inplan view, and has a planar top wall which, in the installed conditionon a vehicle, is substantially horizontal; openings are located adjacentcorners of the top wall; and the top wall forms a lower wall of thelowermost part of the gas flow passage.
 15. The device according toclaim 14, wherein each of the openings includes a flow control valveincorporating a baffle to restrict a flow of water from the chamber tothe gas passage.
 16. The device according to claim 9, wherein openingsfrom a plurality of separate gas flow passages lead into a common waterseparator chamber.